The authors concluded that barley-derived β-glucan appeared to have a beneficial effect on total cholesterol, low density lipid cholesterol and triglycerides, but not on high density lipid cholesterol. In light of unclear quality of included studies and potential for bias in the review process, the authors' conclusions should be treated with caution.

Authors' objectives

To determine the effect of barley-derived β-glucan on lipid parameters in healthy and hypercholesterolaemic adults.

Searching

MEDLINE, EMBASE, CINAHL, Web of Science, The Cochrane Library and Natural Medicines Comprehensive Database were searched from inception to January 2008. Search terms were reported. References of retrieved articles were handsearched.

Study selection

Randomised controlled trials (RCTs) that assessed the impact of barley on total cholesterol, low density lipid cholesterol, high density lipid cholesterol or triglycerides were eligible for inclusion. Crossover trials were eligible for inclusion where there was a four-week washout period; if there was an inadequate washout period, only data from the first phase of the trial was eligible for inclusion.

Included studies assessed pearled barley, barley concentrate, gel barley, barley bran, barley grain or barley flour in β-glucan. Doses ranged (where reported) from 3g to 10g daily over a period that ranged from four to 12 weeks. Most studies included only hypercholesterolaemic participants. In two studies, participants also followed a diet modification.

The authors stated neither how the studies were selected for the review nor how many reviewers performed the study selection.

Assessment of study quality

Methodological quality of included studies was assessed according to whether the study was double-blinded.

Data extraction

For parallel trials, mean changes in lipid levels were extracted for control and intervention groups. For crossover trials, mean difference in values at the end of the intervention and control periods were extracted. Change scores were calculated using the methods of Follman et al.

Two reviewers independently extracted data. Disagreements were resolved by consensus or by a third reviewer.

Methods of synthesis

Weighted mean differences (WMD) with 95% confidence intervals (CI) were calculated using the DerSimonian and Laird model. The Mantel-Haenszel fixed-effect model was also used. Statistical heterogeneity was assessed using the I2 statistic. Publication bias was assessed using funnel plots, Egger's test and the trim and fill method. Sensitivity analyses were conducted. These excluded crossover studies or studies without double-blinding. Subgroup analyses were conducted. These investigated use of concomitant dietary modification and impact on hypercholesterolaemic patients only.

Results of the review

Eight RCTs were included in the review (n=391): five parallel design (n=342); two crossover design with a four-week washout period (n=28); and one crossover design with insufficient crossover period that was treated as a parallel group (n=21). Sample sizes ranged from 10 to 155. Two studies were double-blinded. Three studies were industry funded.

Barley consumption significantly reduced total cholesterol (WMD -13.38mg/dL, 95% CI -18.46 to -8.31; eight studies), low density lipid cholesterol (WMD -10.02mg/dL, 95% CI -14.03 to -6.00; seven studies) and triglycerides (WMD -11.83mg/dL, 95% CI -20.12 to -3.55; six studies) compared to control. High density lipid cholesterol was not significantly reduced by barley consumption compared to control. There was no evidence of significant statistical heterogeneity. The results were not significantly altered when a fixed-effects model was used. There was no evidence of publication bias except for the outcome of total cholesterol (Egger's test p=0.02). When crossover studies and studies that were not double-blinded were excluded, barley no longer significantly reduced triglycerides. Other outcomes were unaffected by sensitivity analyses.

In hypercholesterolaemic patients, barley significantly reduced total cholesterol (WMD -12.56, 95% CI -17.89 to -7.24) and low density lipid cholesterol (WMD -9.38, 95% CI -14.13 to -4.63), but not high density lipid cholesterol or triglycerides, compared to control. The effect of barley on total cholesterol and low density lipid cholesterol was more robust when combined with dietary modification.

Authors' conclusions

Barley-derived β-glucan appeared to have a beneficial effect on total cholesterol, low density lipid cholesterol and triglycerides, but not on high density lipid cholesterol.

CRD commentary

The review addressed a clear question. Inclusion criteria for study design, intervention and outcomes were clearly stated. Inclusion criteria for participants were not reported. It appeared that there was no search for unpublished studies. However, publication bias was investigated and was not assessed to significantly impact on the results. It was unclear whether language restrictions were applied during the search and so language bias could not be ruled out. The authors did not provide any information on control conditions and so it was not possible to ascertain what the intervention was being compared to. Appropriate steps were taken in the data extraction process to minimise reviewer error and bias; it was unclear whether similar steps were taken during study selection and validity assessment. Therefore, reviewer error and bias could not be ruled out definitively. Only one criterion was used to assess methodological quality of included studies. Most included studies were not double-blinded, which undermined study validity. Suitable methods were taken to combine studies. Statistical heterogeneity was assessed and appropriate sensitivity and subgroup analyses were conducted. In light of unclear quality of included studies and potential for bias in the review process, the authors' conclusions should be treated with caution.

Implications of the review for practice and research

Practice: The authors stated that health practitioners may recommend barley for reduction of total and low density lipid cholesterol in hypercholesterolaemic and healthy patients.

Research: The authors stated that larger RCTs were needed to investigate the dose-response relationship between barley and serum lipids.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.